This invention relates to the field of alternator systems and, more particularly, to a multifunction fault detector for use in vehicular alternator systems.
In certain automobile markets, it is desired to provide for the detection and indication of a number of possible alternator system faults by means of a single lamp. Such a system must have, not only reliability, but essentially error-free operation. That is, temporary conditions of overvoltage or undervoltage which are not due to a fault requiring service are to be ignored, and the transient pulses which are normal to automobile ignition systems must not cause false indications.
There are three main fault conditions which it is desirable to detect and indicate; "non-rotation of the alternator", "overvoltage" and "undervoltage". As will be explained hereinafter, there are a number of possible causes for these three indications, but for now it will suffice to say that, for any of these three types of fault, a lamp will be lit with a single accompanying legend such as "CHECK ENGINE". In many designs in the prior art, the detection of "rotation", or apparent lack of alternator output, was done by adding three rectifier diodes to the rectifier stage and detecting the resulting DC or lack thereof. Not only was this method expensive but it was also error-prone since the circuits were sensitive to leakage from the main rectifier diodes.
When detecting an overvoltage condition, it is also important to distinguish between a transient overvoltage condition due, for example, to an abrupt drop in the load with a fully charged battery, and a true overvoltage condition due to an actual fault in the system such as a short-to-ground in the field coil.
When detecting an "undervoltage" condition, it is necessary to distinguish between a temporary low voltage, such as would occur when the load on the system exceeds the generating capacity and pulls the battery voltage down, and an actual fault such as a broken wire between the alternator and the battery.